000
WTNT43 KNHC 040245
TCDAT3

TROPICAL STORM BERTHA DISCUSSION NUMBER  13
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL032014
1100 PM EDT SUN AUG 03 2014

Recent satellite and aircraft reconnaissance data indicate that the
circulation of Bertha has become much better defined this evening.
The tropical cyclone has also quickly strengthened as convection
has increased and become organized in a band around the eastern
portion of the circulation.  An Air Force reconnaissance aircraft
has measured peak believable SFMR winds of around 55 kt. Although
the flight-level winds would support a little lower initial
intensity, a recent dropsonde measured winds in the lowest 150
meters that also supports an initial wind speed of 55 kt.  The
aircraft data also indicate that the minimum pressure has fallen to
around 1007 mb.

The strong northwesterly vertical wind shear that has been affecting
Bertha is forecast to decrease further during the next 24 hours.
This should allow for additional strengthening, and the updated NHC
intensity forecast calls for Bertha to become a hurricane in a day
or so.  In 36 to 48 hours, strong west-southwesterly upper-level
winds are forecast to cause a significant increase in vertical
shear. The shear, along with decreasing sea surface temperatures,
should cause some weakening before Bertha becomes an extratropical
low over the North Atlantic in three to four days.

Bertha is moving north-northwest at 15 kt.  The cyclone should turn
northward and then north-northeastward during the next day or so
while it moves between a subtropical high to its east and a mid- to
upper-level trough over the eastern United States.  In a couple of
days, Bertha is expected to accelerate northeastward and then turn
east-northeastward when it moves into the mid-latitude westerlies.
The model guidance is generally in good agreement on this scenario
through 72 hours, and the new NHC track forecast is similar to the
previous advisory during that time.  There is increasing spread in
the track guidance after three days with the ECMWF and UKMET models
predicting a much faster motion over the North Atlantic than the
latest GFS.  The four- and five-day forecast positions are close to
the model consensus and guidance provided by the NOAA Ocean
Prediction Center.


FORECAST POSITIONS AND MAX WINDS

INIT  04/0300Z 24.9N  73.2W   55 KT  65 MPH
 12H  04/1200Z 27.3N  73.7W   60 KT  70 MPH
 24H  05/0000Z 30.8N  73.4W   65 KT  75 MPH
 36H  05/1200Z 34.1N  72.0W   65 KT  75 MPH
 48H  06/0000Z 36.9N  69.0W   65 KT  75 MPH
 72H  07/0000Z 42.2N  59.5W   60 KT  70 MPH
 96H  08/0000Z 47.5N  50.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  09/0000Z 49.5N  40.0W   50 KT  60 MPH...POST-TROP/EXTRATROP

$$
Forecaster Brown